Often times it is desirable to insure that a computer workstation remains unaltered, even though it is being used by a multitude of users in potentially varied and unknown ways. For example, in public environments such as schools, libraries, and other community facilities, access to a group of computer systems is highly desired, for example, to conduct research, use common resources of a company, or to learn and try new programs. Typically, these environments can be characterized as having “uncontrolled access,” because the moment by moment usage of the computer systems is not monitored.
In such situations, it is highly desirable to insure that users can utilize the functionality of the computer system but not be allowed to “corrupt” the persistent storage of the system, so that follow-on users will find the system in a pristine state. One mechanism for preventing such corruption is to make a copy of the pristine state of the computer system desired and to restore the copy prior to shutdown of the system by each user. One difficulty with such an approach is that it is often difficult in operating system environments to capture the hardware on/off switch, and so, when a user cycles power without a proper operating system shutdown, the system is unable to successfully restore the pristine state.
Some systems have used special hardware cards to perform the copying. For example, one such system copies the pristine state of the disk storage device into a special disk partition before use access is permitted. Data from the special disk partition is then copied back (restored) upon computer system shut down.
In database environments, other techniques have been used. Typically, for example, the database changes (in opposite order) are “undone” to the storage device to return it to a pristine state. This technique also suffers from failure in the cycle power situation.